On a generalized vector equilibrium problem with bounds

We prove the existence of a solution to the generalized vector equilibrium problem with bounds. We show that several known theorems from the literature can be considered as particular cases of our results, and we provide examples of applications related to best approximations in normed spaces and variational inequalities.     

In-depth analysis of the mathematical model of polyester thermosets curing

In many areas of chemical engineering applications we have to deal with thermosetting polymer structures. One of the major processing techniques for producing such structures is the curing process. This process may be accompanied by undesirable thermal spiking phenomena during which the released energy may be trapped inside the structure. In order to predict the onset of this phenomenon models that couple reaction kinetics and heat transfer are required. The numerical model was constructed by taking into account the heat transferred by conduction through the resin, as well as the kinetics of heat generated by the cure reaction. The contributions to the rise in temperature from heat conduction and chemical reactions are different in different parts of the composite, which can be explained by the temperature–time, or conversion-time histories. The temperatures were measured in the center of a cylindrically shaped mold. Initiator concentration varied from 0.5% to 2.0% of mass fraction throughout the experiments, which governed the reaction kinetics. Introduction of the carbon base filler reduced the amount of heat generated in the composite, and as a result lowered the temperatures of the resin. The analysis of parameter sensitivity and model simulation was performed with data obtained. A good agreement was observed between experimental data and the mathematical model of the curing process in the mold.     

EPMA and Microstructural Characterization of Yttrium Doped BaTiO3 Ceramics

 Yttrium-doped BaTiO₃ ceramics have been studied as a potential material for positive temperature coefficient resistors (PTCR). The mechanism of Y incorporation into BaTiO₃ plays an important role for displaying good electrical properties. Determination of the amount of yttrium in the BaTiO₃ as well as microstructure characterization of the samples were performed using SEM, EDS and WDS analysis. An optimized trace element WDS quantitative analysis was applied to determine elemental concentrations for Ba, Ti and Y in the samples as accurately as possible. BaTiO₃ and Y₂O₃ were used as standards. Analysis was undertaken using a JEOL JXA 840A electron probe microanalyzer. WDS X-ray intensity measurements were performed under 20 kV, 50 nA beam current and 0.2% preset standard counting deviation (σ_c) using a PET crystal. Measured k-ratios were quantified by ZAF matrix correction. Average results of WDS quantitative analysis showed 20.17 ± 0.08 at % Ti, 19.95 ± 0.09 at % Ba, 0.22 ± 0.03 at % Y, and 59.66 at % O. The results suggest incorporation of yttrium in the BaTiO₃ preferentially at the Ba-sites, however partial incorporation of Y at Ti-sites could not be excluded.     

Kinetics of gas oil catalytic cracking

Summary In the present work catalytic cracking of gas oils has been studied in a standard MAT reactor. The cracking product distribution was measured at four different temperatures. Based on the experimental results, a 4-lump kinetic model was applied. Kinetic constants were estimated using the sequential step optimization method. Simulation results have shown to be in a good agreement with experimental data. An isothermal pseudo steady-state model for fixed bed MAT reactor is proposed.     

On the structure of kripke models of heyting arithmetic

Since in Heyting Arithmetic (HA) all atomic formulas are decidable, a Kripke model for HA may be regarded classically as a collection of classical structures for the language of arithmetic, partially ordered by the submodel relation. The obvious question is then: are these classical structures models of Peano Arithmetic (PA)? And dually: if a collection of models of PA, partially ordered by the submodel relation, is regarded as a Kripke model, is it a model of HA? Some partial answers to these questions were obtained in [6], [3], [1] and [2]. Here we present some results in the same direction, announced in [7]. In particular, it is proved that the classical structures at the nodes of a Kripke model of HA must be models of IΔ₁ (PA^- with induction for provably Δ₁ formulas) and that the relation between these classical structures must be that of a Δ₁-elementary submodel. MSC: 03F30, 03F55.     

Assembly and charge transfer in hybrid TiO(2) architectures using biotin-avidin as a connector

Exploiting the presence of undercoordinated surface Ti atoms at the tips of TiO2 nanorods and the dopamine selectivity for these Ti surface states, biotin was conjugated to TiO2 nanocrystallites using dopamine as a bridging linker. Using abiotin-avidin complex as a connector the "tip-to-tip" assembly of 400 nm elongated TiO2 rods was obtained. The photoexcitation of avidin-TiO2 hybrids resulted in the transfer of holes from nanocrystallites to protein and consequent oxidation of avidin, most probably at tyrosine 33.     

Spin label EPR-based characterization of biosystem complexity

Following the widely spread EPR spin-label applications for biosystem characterization, a novel approach is proposed for EPR-based characterization of biosystem complexity. Hereto a computational method based on a hybrid evolutionary optimization (HEO) is introduced. The enormous volume of information obtained from multiple HEO runs is reduced with a novel so-called GHOST condensation method for automatic detection of the degree of system complexity through the construction of two-dimensional solution distributions. The GHOST method shows the ability of automatic quantitative characterization of groups of solutions, e.g. the determination of average spectral parameters and group contributions. The application of the GHOST condensation algorithm is demonstrated on four synthetic examples of different complexity and applied to two physiologically relevant examples--the determination of domains in biomembranes (lateral heterogeneity) and the study of the low-resolution structure of membrane proteins.     

An EPMA Study on KNbO3 and NaNbO3 Single Crystals – Potential Reference Materials for Quantitative Microanalysis

Single crystals of KNbO₃ and NaNbO₃ were selected from the limited number of suitable alkali compounds that are available and evaluated as possible reference materials for the electron-probe microanalysis (EPMA) of alkaline niobates with a composition described by the general formula K_1–XNa_XNbO₃. The EPMA study verified that KNbO₃ and NaNbO₃ single crystals are stable under the electron beam and compositionally homogeneous. A quantitative microanalysis confirmed the composition of pure KNbO₃, while the NaNbO₃ crystal contained 0.3 mass fraction % of Ca. A significant improvement in the accuracy of the quantitative EPMA of polycrystalline potassium–sodium niobates was achieved using these single crystals as standards. The crystals can also be useful as reference materials for the analysis of sodium and potassium in other materials.